Artem Kuzmin

Physical mechanisms of timing jitter in photon detection by current-carrying superconducting nanowires

We studied timing jitter in the appearance of photon counts in meandering nanowires with different fractional amount of bends. Timing jitter, which is the probability density of the random time delay between photon absorption in current-carrying superconducting nanowire and appearance of the normal domain, reveals two different underlying physical scenarios. In the deterministic regime, which is realized at large currents and photon energies, jitter is controlled by position dependent detection threshold in straight parts of meanders and decreases with the current. At small photon energies, jitter increases and its current dependence disappears. In this probabilistic regime jitter is controlled by Poisson process in that magnetic vortices jump randomly across the wire in areas adjacent to the bends.

Operation of Superconducting Nanowire Single-Photon Detectors Embedded in Lumped-Element Resonant Circuits

We propose a new operation principle for superconducting nanowire single-photon detectors (SNSPDs) enabling an efficient frequency-division multiplexing of the bias and readout signals of a large multipixel detector array. The SNSPD is part of a resonant circuit, and the microwave signal inside the device is used to bias the detector close to the critical state. Hence, an n×m pixel SNSPD array requires only two coaxial cables from room temperature to the detector ambient temperature of 4.2 K. We show the microwave characterization and single-photon response of such devices and compare the detector efficiencies with conventional dc-biased SNSPDs. Furthermore, we demonstrate the feasibility of array applications with the new operation mode in a two-pixel proof-of-principle device.

Frequency-multiplexed bias and readout of a 16-pixel superconducting nanowire single-photon detector array

We demonstrate a 16-pixel array of microwave-current driven superconducting nanowire single-photon detectors with an integrated and scalable frequency-division multiplexing architecture, which reduces the required number of bias and readout lines to a single microwave feed line. The electrical behavior of the photon-sensitive nanowires, embedded in a resonant circuit, as well as the optical performance and timing jitter of the single detectors is discussed. Besides the single pixel measurements, we also demonstrate the operation of a 16-pixel array with a temporal, spatial, and photon-number resolution.

Wide-Range Bolometer With RF Readout TES

To improve both scalability and noise-filtering capability of a transition-edge sensor (TES), a new concept of a thin-film detector is suggested, which is based on embedding a microbridge TES into a high-Q planar GHz-range resonator weakly coupled to a 50-Ω-readout transmission line. Such a TES element is designed as a hot-electron microbolometer coupled to a THz-range antenna and as a load of the resonator at the same time. A weak THz signal coupled to the antenna heats the microbridge TES, thus reducing the quality factor of the resonator and leading to a power increment in the readout line. The power-to-power conversion gain, an essential figure of merit, is estimated to be above 10. To demonstrate the basic concept, we fabricated and tested a few submicrometer-sized devices from Nb thin films for operation temperature about 5 K. The dc and RF characterization of the new device is made at a resonator frequency about 5.8 GHz. A low-noise high-electron mobility transistor amplifier is used in our TES experiments without the need for a SQUID readout. The optical sensitivity to blackbody radiation within the frequency band 600-700 GHz ismeasured as (2.7 ± 0.9) × 10-14 W/√Hz at Tc ≈ 5 K at bath temperature ≈1.5 K.

Investigation of the Electrical Field Sensitivity of Sub-μm Y–Ba–Cu–O Detectors

The behavior of submicrometer-sized thin-film YBa2Cu3O7-x (YBCO) detectors under illumination with picosecond terahertz (THz) pulses was investigated. Real-time measurements with a temporal resolution of 15 ps full width at half maximum were performed at ANKA, the synchrotron facility of Karlsruhe Institute of Technology, and the UVSOR-III facility at the Institute for Molecular Science in Okazaki, Japan. The capability of YBCO detectors to reproduce the shape of a several picosecond long THz pulse was demonstrated. Single-shot measurements adhering to a reversal of the direction of the electrical field of the THz radiation were carried out. They provided evidence for the electrical field sensitivity of the YBCO detector. Exploiting the electrical field sensitivity of the YBCO detector, the effect of microbunching was observed at UVSOR-III.

Progress in Development of the Superconducting Bolometer With Microwave Bias and Readout

Our new detector and readout concept brings together TES (Transition Edge Sensor) and MKID (Microwave Kinetic Inductance Detector) technologies and exploits the idea of a microwave-induced superconducting transition in a small thin-film microbridge. The superconducting transition of the bridge manifests itself as variation in the Q -factor of niobium resonators at 5–8 GHz, somewhat similar to MKID operation. We present data showing the potential for developing this concept into multipixel detector arrays. Single-pixel sensitivity was measured at 4.5 K for an input band of 600–700 GHz using a prototype 10-nm-thick Nb bridge of size 1 μm × 500 nm. Radiation from human skin was detected with a resolution better than 1 K/rtHz, which is encouraging for terahertz imaging applications. To further improve device sensitivity, we are also developing Hf-based devices that operate near 0.35 K. Details about the physics and stability of these devices are discussed.

Enhancement of superconductivity in NbN nanowires by negative electron-beam lithography with positive resist

We performed comparative experimental investigation of superconducting NbN nanowires which were prepared by means of positive- and negative electron-beam lithography with the same positive tone Poly-methyl-methacrylate (PMMA) resist. We show that nanowires with a thickness 4.9 nm and widths less than 100 nm demonstrate at 4.2 K higher critical temperature and higher density of critical and retrapping currents when they are prepared by negative lithography. Also the ratio of the experimental critical current to the depairing critical current is larger for nanowires prepared by negative lithography. We associate the observed enhancement of superconducting properties with the difference in the degree of damage that nanowire edges sustain in the lithographic process. A whole range of advantages which is offered by the negative lithography with positive PMMA resist ensures high potential of this technology for improving the performance metrics of superconducting nanowire singe-photon detectors.

Proximity effect model of ultranarrow NbN strips

We show that narrow superconducting strips in superconducting (S) and normal (N) states are universally described by the model presenting them as lateral NSN proximity systems in which the superconducting central band is sandwiched between damaged edge-bands with suppressed superconductivity.The width of the superconducting band was experimentally determined from the value of magnetic field at which the band transits from the Meissner state to the static vortex state. Systematic experimental study of 4.9 nm thick NbN strips with widths in the interval from 50 nm to 20

Integrated Four-Pixel Narrow-Band Antenna Array for Picosecond THz Spectroscopy

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Development of high-sensitive 1.2 mm imaging radiometer with two-polarization antenna-coupled TES-bolometer array for ground-based 6-m optical telescope

m, which are all smaller than the Pearls length, demonstrates gradual evolution of the temperature dependence of the critical current with the change of the strip width.